Septic shock is a life-threatening complication of bacterial infection. The reported number of incidences has steadily increased since the 1930's, and septic shock is presently the most common cause of mortality and morbidity in non-coronary intensive care units in the U.S. The yearly mortality due to septic shock in the U.S. is as high as 200,000.
Bacteremia is typically defined as bacteria in the bloodstream and is usually determined by a positive blood culture. Sepsis refers to the physiological alterations and clinical consequences of the presence of microorganisms or their products in the bloodstream or tissues. When sepsis is associated with hypotension and signs of poor tissue perfusion, it is called septic shock. Septic shock has traditionally been recognized as a consequence of infection with gram-negative bacteria, but it may also be caused by gram positive bacteria, fungi, viruses, and protozoa.
The pathogenesis of septic shock is complex and not fully understood. One of the complicating factors is that overlapping, and sometimes even opposing, effects can be present. Various gram-negative microorganisms can generate endotoxins which can release potential mediators such as IL-1 and TNF-.alpha. that would act on vasculature and myocardium. Studies in both animals and humans have shown that endotoxin is the primary factor that precipitates the shock state. Endotoxin is a lipopolysaccharide molecule that is contained in the cell wall of all gram-negative bacteria. It is released from a focus of infection when gram-negative bacteria are phagocytized by either circulating macrophages or cells of the reticuloendothelial system.
In the past, the conventional approach in treating septic shock has been to administer intravenous injection of excess amounts of glucocorticolds, such as methylprednisolone, at dosage of about 30 mg per kilogram of body weight. However, this method has been proven ineffective in two double-blind control studies.
It has long been known that endotoxins activate the complement cascade, and, via the release of components of the complement system, many of the effects of sepsis occur. After invading the bloodstream, microorganisms begin a cascade of events leading to the release of microbial toxins and harmful host mediators that produce sepsis. The early mediators are thought to consist of microorganism-oriented exotoxins and endotoxins, and host effectors such as neutrophils and macrophages, which produce cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1). The release of cytokines in small amounts is normally a protective response. In the presence of endotoxins, however, the massive release of TNF and subsequent activation of immune cells can lead to persistent uncontrolled systemic inflammation, resulting in wide tissue injury and metabolic derangement.
Once released, cytokines trigger a complex array of further host substances, such as prostaglandins, coagulative and fibrinolytic cascades, nitric oxide (NO), endorphins, interferons, and platelet-activating factors. Overall, this network of mediators and toxins affect the systemic and pulmonary vasculatures, the myocardium, and the structures of endothelium, producing hypotension and resulting in death. NO is a potent endothelium-derived relaxing factor (EDRF); it may play a major role in the regulation of microcirculation. In the past, in vitro and in vivo studies have suggested that endotoxin-induced loss of vascular responsiveness is due to activation of NO which is synthesized from L-arginine and can be blocked by NO synthase inhibitors, L-arginine analogues, such as N-nitro-L-arginine methyl ester (L-NAME). Several studies have shown that NO has a major effect on cardiovascular performance in endotoxemia. Inhibition of NO synthesis has thus been considered as being a potentially useful method in the treatment of sepsis.
None of the prior art methods have a proven record of success. Therefore, other therapies must be considered to improve survival rate and reduce morbidity. In recent years, immunotherapy and immunoprophylaxis have been advocated, and it has been suggested that human antiserum and monoclonal antibodies can be effective against endotoxins and TNF reduced death from gram-negative bacterial infection.
Several U.S. patents have discussed the prophylaxis and treatment of endotoxin-induced shock. U.S. Pat. No. 4,388,318 ('318 patent) issued to Kayama, et al, discloses a method of treating endotoxin shock with a pyrimido-pyrimidine derivative. The basis of the '318 patent is that central adrenergic neurons influence peripheral sympathetic nerve activity and thus cardiovascular regulation. The inhibition of alpha adrenergic receptors in vasomotor centers mediates a decrease in blood pressure, heart rate and peripheral sympathetic activity. Since E. coli endotoxin may exert its hypotensive effect by activating the central autonomic blood pressure regulatory circuits, the administering of a pyrimido-pyrimidine derivative, which has a central hypertensive effect acting on the medullary cardiovascular regulatory systems, may stimulate central alpha adrenergic receptors leading to inhibition of brain stem sympathetic pathways that participate in the baroreceptor reflex system.
U.S. Pat. No. 4,822, 776 ('776 patent), issued to Ceraml and Kawakami, discloses an endotoxin-induced mediator substance, which purportedly may be utilized as a screening agent to test for potentially effective anti-shock agents. In the '776 patent, it was suggested that the mediator substance can be used to produce antibodies to themselves in rabbits, goats, sheep, chickens, or other mammals. These antibodies may be used as test agents for the presence of the mediator substance, and can be administered in pharmaceutical compositions in response to shock produced by viruses, bacteria, protozoa, etc.
U.S. Pat. No. 5,028, 627 ('627 patent) discloses a method of using arginine derivatives as arginine antagonists for prophylaxis or treatment of systemic hypertension associated with nitric oxide production or endothelial derived relaxing factor. One embodiment of the inhibitor disclosed in the '627 patent is N.sup.G -substituted arginine or an N.sup.G,N.sup.G -disubstituted arginine, which is administered to an animal that is potentially developing or having a systemic hypotension induced by a biological response modifier. The '627 patent follows the commonly accepted belief that arginine is the physiological precursor of nitric oxide synthesis, and concludes that substituted or disubstituted arginine antagonists, such as N.sup.G -aminoarginine, N.sup.G -nitroarginine, N.sup.G -methylarginine, N.sup.G -ethylarginine, N.sup.G -propylarginine, N.sup.G -butylarginine, etc., could inhibit the production of nitrogen oxide from arginine in an animal or patient, thus obviating the hypotensive effects of nitrogen oxide.
U.S. Pat. No. 5,068,314 discloses an arginine derivative, which functions as a lipopolysaccharide-binding polypeptide, for removing endotoxin. U.S. Pat. No. 5,175,183 discloses the use of lipoxygenase-inhibiting compounds in treating disease states, including endotoxin shock. The compounds disclosed include N-aryl, N-heteroaryl, N-arylalkyl, N-heteroarylalkyl, N-arylcyclopropyl, and N-heteroaryl-cyclopropyl-N'-hydroxyurea compounds. U.S. Pat. No. 5,171,739 discloses a method for treating and preventing endotoxin-associated shock using a BPI protein that is effective in binding endotoxins. U.S. Pat. No. 5,162,571 discloses phenol derivatives that have therapeutic and prophylactic activities against endotoxin shock.
As indicated above, traditional approaches to the treatment of septic shock have mainly involved administering glucocorticoids, LPS-antibodies, NO-synthase inhibitors, and arginine derivatives (as arginine antagonists). However, none of these methods has been proven clinically effective. One of the most difficult problems in developing an effective treatment method lies in the fact that the mechanisms causing the endotoxin-induced shocks have not been fully understood, or may have been incorrectly stated.
It has previously been discovered that several compounds can effectively prevent the occurrence of endotoxin-induced shock. U.S. Pat. No. 5,436,270 ('270 patent) discloses arginine, which, when intraperitorially injected 24 hours prior to lipopolysaccharide injection, can significantly prevent lipopolysacchande-induced mortality. U.S. Pat. No. 5,502,055 and U.S. Pat. No. 5,576,350 disclose putrescine and spermidine, respectively, which when administered in a manner similar to that used for arginine, can also significantly prevent lipopolysaccharide-induced mortality.